Bone attachment structure with engagement projections

ABSTRACT

Fixed and polyaxial bone attachment assemblies include a receiver with a pair of spaced arms defining a open channel for receiving a longitudinal connecting member. Inner surfaces of the arms have a flangeform discontinuous guide and advancement structure for receiving a closure structure, the longitudinal connecting member being captured in the receiver by the closure structure. The longitudinal connecting member receiving surface includes a bottom seat disposed opposite an opening of the channel and a pair of curved substantially opposed side surfaces facing toward one another on either side of the bottom seat. At least one projection extends from one of the side surfaces, the projection having a sharp end. Upon assembly with a longitudinal connecting member, such as a cylindrical rod, the projection sharp end engages and penetrates the surface of the longitudinal connecting member, guarding against translational and rotational movement of the rod within the receiver. The projection or projections are disposed either directly on a receiver or on a compression insert pre-loaded into the receiver.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 11/140,343 filed May 27, 2005, incorporated by reference herein. This application is also a continuation-in-part of U.S. patent application Ser. No. 11/178,854 filed Jul. 11, 2005 that claims the benefit of U.S. Provisional Application No. 60/655,239 filed Feb. 22, 2005, both of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention is directed to open fixed and polyaxial bone attachment structures including screws and other anchors for use in bone surgery, particularly spinal surgery and particularly to such bone attachment structures for engagement with a longitudinal connecting member.

Bone screws are utilized in many types of spinal surgery, such as for osteosynthesis, in order to secure various implants to vertebrae along the spinal column for the purpose of stabilizing and/or adjusting spinal alignment. Although both closed-ended and open-ended bone screws are known, open-ended screws are particularly well suited for connections to longitudinal connecting members such as rods, and also to connector arms, because such rods or arms do not need to be passed through a closed bore, but rather can be laid or urged onto the open receiver channel of an open ended bone screw.

Typical open-ended bone screws include a threaded shank with a pair of parallel projecting branches or arms which form a yoke with a U-shaped slot or channel to receive an elongate longitudinal connecting member, such as a solid rod, hollow cylinder or coil-like member. Hooks and other types of connectors, as are used in spinal fixation techniques, may also include open ends for receiving elongate longitudinal connecting members.

A common mechanism for providing vertebral support is to implant bone screws into certain bones which then in turn support a longitudinal structure such as a rod, or are supported by such a rod. Bone screws of this type may have a head or receiver that receives the rod or other structure that is fixed relative to a shank thereof. In the fixed bone screws, the fixed receiver cannot be moved relative to the shank and the rod must be favorably positioned in order for it to be placed within the receiver. Open-ended polyaxial bone screws allow rotation of a rod receiver with respect to the shank until a desired rotational position of the receiver is achieved relative to the shank. A rod is inserted into the receiver and eventually the receiver is locked or fixed in a particular position relative to the shank.

There are a variety of ways in which the rod may be captured within an open bone screw. Some sort of closure structure or plug is required so as to block the channel opening once the rod is inserted therein and, also preferably urge the rod into a seated and locked position relative to the receiver. A substantial amount of torque is required to seat the plug against the rod which in turn seats the rod in the receiver channel so as to prevent relative motion between the rod and the bone screw. Consequently, the need to highly torque a plug disposed between the arms of an open bone screw functions counter to the need to prevent the bone screw arms from splaying.

Certain prior art plug type closures have been threadably received between the opposed arms of the bone screw receiver using conventional V-shaped thread forms which has resulted in a significant amount of radially outward pressure or force being applied to the arms of the bone screw receiver. Such outward force may result in splaying of the arms, after which the closure becomes loose which may either result in a failure of the implant by allowing the rod to slip relative to the bone screw or the closure may even come completely out of the receiver of the bone screw for total failure of the implant. In order to help relieve this problem, certain of the prior art has added structure to the rod engaging lower surface of the closure. Such structure has included adding a central or axial point or ring designed to penetrate into the rod and help lock the rod into place. Surface finish on the plug, such as knurling, has also been utilized.

During use, spinal implants, especially those designed for use with injured or diseased vertebrae often undergo substantial stress, even during simple everyday body movement. Thus it is important for the various spinal implant components to remain in the relative positions in which they were placed by the surgeon so as to maintain proper placement and alignment of the vertebrae. Thus, it is desirable to hold a longitudinal connecting member in place within a bone screw or anchor, with respect to both translational axial movement and with respect to rotation relative to the bone screw or anchor. Structure, such as the “point and rim construction” previously described herein, that partially penetrates a longitudinal connecting member is helpful in that regard.

At a side of the rod opposite of the closure plug, various compression spacers or insertable compression structures have been developed that are operably disposed adjacent the rod and within the bone screw receiver. Such compression structures have been used to frictionally link the rod with the bone screw shank and to aid in snugly seating the rod in the open bone screw, thus aiding in preventing relative motion between the rod and the bone screw. Prior art bone screw compression inserts have typically been utilized with top-loaded bone screw shanks, having substantially spherical heads that are integral with the shank body. Such compression inserts include those that contact an upper spherical portion of the bone screw shank and others that extend substantially around such a spherical surface. Such compression inserts may also include a curved upper surface or surfaces for receiving the rod.

Bone screw compression inserts may desirably reduce some of the relative motion between the rod and the bone screw, but may be undesirable in practice as they may also require separate insertion during surgery, after implantation of the bone screw shank, and may be small and thus difficult to handle. Alternatively, compression inserts loaded in a bone screw prior to implantation may obstruct bone screw features utilized for driving the threaded bone screw shank into bone, or require less than desirable modifications in the bone screw, decreasing strength and/or requiring specialized driving tools.

SUMMARY OF THE INVENTION

Fixed and polyaxial bone attachment assemblies according to the invention include a receiver with a pair of spaced arms defining a open channel for receiving a longitudinal connecting member. Inner surfaces of the arms have a discontinuous guide and advancement structure for receiving a closure structure, the longitudinal connecting member being captured in the receiver by the closure structure. The longitudinal connecting member receiving surface includes a bottom seat and a side surface disposed laterally of the bottom seat, the side surface having at least one projection. Typically, a pair of substantially opposed side surfaces are disposed on either side of the bottom seat and face the open channel with at least one projection extending from one or both of the side surfaces, the projection having a sharp end. Upon assembly with a longitudinal connecting member, such as a cylindrical rod, the projection sharp end engages and preferably penetrates the surface of the longitudinal connecting member, guarding against translational and rotational movement of the rod within the receiver.

According to one aspect of the invention, the sharp end or point of the projection is directed substantially radially inwardly toward an axis of a longitudinal connecting member when the connecting member is received in the channel and pressed toward the bottom seat by a closure structure. According to another aspect of the invention, up to a plurality of projections are disposed on the side surfaces, preferably evenly spaced and positioned facing one another on either side surface. The projections may either be directly on a rod receiving surface of the receiver or on a compression insert disposed in the receiver wherein the bone attachment structure is a polyaxial bone screw having a shank with an upper portion disposed in the receiver, the upper portion having a formation sized and shaped for engagement with a bone screw driver for driving the shank into bone, and the compression member having an aperture sized and shaped for receiving the driver therethrough. It is foreseen that the plurality of projections on a compression insert may include a knurled or high friction surface.

According to another aspect of the invention, the bone attachment structure is a fixed bone screw with up to a plurality of pointed projections extending radially inwardly from the receiver surface.

According to a further aspect of the invention, the projections are integral with either the bone screw receiver or the compression insert. Further according to the invention, the projection or projections are attachable and removable from the longitudinal connecting member receiving surface of the bone attachment structure.

A polyaxial bone screw according to the invention includes a shank having an upper portion and a body for fixation to a bone. The assembly further includes an independent non-integral retainer structure for holding the shank upper portion within the receiver. Furthermore, a compression structure having at least one projection directed radially inwardly is operably disposed between the retaining structure and the rod. The shank upper portion is supported in the receiver by the retaining structure. The retainer structure can be operably and slidably in contact with an inner surface of the receiver, allowing the shank body to be swivelable with respect to the receiver.

Further according to the invention, a closure structure having a flangeform thereon is mateable with cooperating flange-form structure on inner arms of an upper portion of a receiver of a bone attachment structure of the invention. The closure member further includes a flat or dome-shaped lower surface for operably pressing against the rod or other longitudinal connecting member or other structural member. The rod in turn contacts and presses on the compression structure with projections of the compression structure piercing the rod, and the compression structure contacts and presses on the retaining structure which fixes the retaining structure against an inner seating surface of the receiver.

OBJECTS AND ADVANTAGES OF THE INVENTION

Therefore, objects of the present invention include: providing an improved spinal implant assembly for implantation into vertebrae of a patient; providing such an assembly that includes a receiver connected to a shank, the receiver forming a channel for receiving an elongate longitudinal member, a surface forming the channel having at least one outwardly extending projection pointing radially toward an axis of the longitudinal connecting member, the projection for frictional engagement with the longitudinal connecting member; providing such an assembly wherein the projection is a point that penetrates the longitudinal connecting member; providing such an assembly wherein the point is integral with the receiver; providing such an assembly wherein the point is removable; providing such points of varying size, hardness and sharpness; providing such an assembly with a point adaptable for use with any type of bone anchor including open, closed, fixed and polyaxial bone screws; providing such an assembly that includes a receiver with an open channel, a shank pivotally connected to the receiver, a rod or other structural element, and a compression structure disposed between the shank and the rod, the compression structure having at least one pointed projection for frictionally engaging and/or penetrating the shank; providing such an assembly that has a low profile after final installation; providing such an assembly in which the compression structure may be inserted into a bone screw receiver prior to installing the bone screw into bone; providing such an assembly in which an upper shank portion of the bone screw includes a non-slip feature for driving the shank into bone; providing such an assembly in which an upper portion of the bone screw shank has a maximum diameter or width that is smaller than a diameter or width of a lower opening of the bone screw receiver and further includes an independent retaining structure to keep the shank upper portion within the bone screw receiver; and providing such an assembly that is easy to use, especially adapted for the intended use thereof and wherein the implant assembly components are comparatively inexpensive to produce.

Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.

The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an assembly according to the invention including a shank with a capture structure at one end thereof, a receiver, a retaining structure and a compression structure with a plurality of radially extending pointed projections.

FIG. 2 is an enlarged front elevational view of the compression structure of FIG. 1.

FIG. 3 is an enlarged top plan view of the compression structure of FIG. 1.

FIG. 4 is an enlarged bottom plan view of the compression structure of FIG. 1.

FIG. 5 is an enlarged, exploded front elevation of the shank and retaining structure of FIG. 1.

FIG. 6 is a partial cross-sectional view of the shank and retaining structure taken along the line 6-6 of FIG. 5.

FIG. 7 is an enlarged and partial view of the shank and retaining structure of FIG. 6.

FIG. 8 is an enlarged and partial cross-sectional view of the receiver taken along the line 8-8 of FIG. 1 and showing a first stage of insertion of the compression structure.

FIG. 9 is an enlarged and partial cross-sectional view of the receiver similar to FIG. 8 and showing a fully installed compression structure.

FIG. 10 is a top plan view of the bone screw receiver, shank, retaining structure and compression structure of FIG. 9.

FIG. 11 is a cross-sectional view of the receiver, shank, retaining structure and compression structure, shown being driven into a vertebra with an Allen-type tool.

FIG. 12 is a partial cross-sectional view similar to FIG. 11 further showing a rod and a partially installed closure structure, also in cross-section.

FIG. 13 is a partial cross-sectional view similar to FIG. 12 showing a break-off head of the closure structure removed.

FIG. 14 is an enlarged and partial cross-sectional view taken along the line 14-14 of FIG. 13.

FIG. 15 is an exploded and partial perspective view of an alternative implant assembly according to the invention having a fixed bone screw according to the invention with a shank integral with an open receiver and shown with a longitudinal connecting member and a closure structure.

FIG. 16 is an enlarged top plan view of the bone screw of FIG. 15.

FIG. 17 is an enlarged and partial front elevational view of the bone screw of FIG. 15.

FIG. 18 is an enlarged and partial cross-sectional of the implant assembly of FIG. 15 shown assembled and taken along the line 18-18 of FIG. 15.

FIG. 19 is a reduced and partial cross-sectional view similar to FIG. 18 with a break-off head of the closure structure removed.

FIG. 20 is an enlarged and partial side elevational view of the assembly of FIG. 19 with portions removed to show the detail thereof.

FIG. 21 is an exploded and partial perspective view of another alternative embodiment of an implant assembly according to the invention having a second fixed bone screw according to the invention with a shank integral to a receiver and shown with a longitudinal connecting member and a closure structure.

FIG. 22 is an enlarged top plan view of the bone screw of FIG. 21.

FIG. 23 is an enlarged and partial front elevational view of the bone screw of FIG. 21.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure.

With reference to FIGS. 1-14, the reference numeral 1 generally designates a polyaxial bone screw assembly according to the present invention. The assembly 1 includes a shank 4 that further includes a body 6 integral with an upwardly extending, substantially cylindrical end portion or capture structure 8; a receiver or head 10; a retaining structure 12; and a compression structure 14 having at least one and up to a plurality of radially inwardly extending pointed or sharply edged projections or cleats 15. The shank 4, the receiver 10, the retaining structure 12 and the compression structure 14 are preferably assembled prior to implantation of the shank body 6 into a vertebra 16, which procedure is shown in FIG. 11 and will be discussed more fully below.

FIGS. 12-14 further show a closure structure generally 18, of the invention for capturing a longitudinal member such as a rod 21 within the receiver 10. Upon installation, which will be described in detail below, the closure structure 18 presses against the rod 21 that in turn presses against the compression structure 14 that presses against the retaining structure 12 that is threadably mated in this embodiment to the shank end portion or capture structure 8. As the rod 21 presses against the compression structure 14, the projections 15 abrade and penetrate the rod surface. The compression structure 14 biases the retaining structure 12 into fixed frictional contact with the receiver 10, so as to fix the rod 21 relative to the vertebra 16. The receiver 10, shank 4, retaining structure 12 and compression structure 14 cooperate in such a manner that the receiver 10 and shank 4 can be secured at any of a plurality of angles, articulations or rotational alignments relative to one another and within a selected range of angles both from side to side and from front to rear, to enable flexible or articulated engagement of the receiver 10 with the shank 4 until both are locked or fixed relative to each other. The bone screw assembly 1 and the closure structure 18 and associated driving tools may be constructed of any suitable bio-compatible material. Stainless steel and titanium are particularly preferred materials because of their strength and suitability for surgical use and implantation.

The shank 4, best illustrated in FIGS. 1 and 5-7, is elongate, with the shank body 6 having a helically wound, radially outwardly extending bone implantable thread 22 axially extending from near a tip 24 of the body 6 to near a slanted or sloped surface 26 that is adjacent to a lateral projection illustrated as a smooth cylindrical surface 28 located adjacent to the capture structure 8. As will be described more fully below for the embodiment shown, the laterally projecting cylindrical surface 28 includes a buttress stop feature 30 for frictional engagement with and placement of the retaining structure 12. During use, the body 6 utilizing the thread 22 for gripping and advancement is implanted into the vertebra 16 leading with the tip 24 and driven down into the vertebra 16 with an installation or driving tool so as to be implanted in the vertebra 16 to near the sloped surface 26, as shown in FIGS. 12-14, and as is described more fully in the paragraphs below. The shank 4 has an elongate axis of rotation generally identified by the reference letter A. It is noted that any reference to the words top, bottom, up and down, and the like, in this application refers to the alignment shown in the various drawings, as well as the normal connotations applied to such devices, and is not intended to restrict positioning of the assembly 1 in actual use.

The sloped surface 26 extends radially outward and axially upward from the shank body 6 to the cylindrical projection 28. Further extending axially from the projection 28 is the capture structure 8 that provides a connective or capture apparatus disposed at a distance from the threaded shank body 6 and thus at a distance from the vertebra 16 when the body 6 is implanted in the vertebra 16.

The capture structure 8 is configured for connecting the shank 4 to the receiver 10 and capturing the shank 4 in the receiver 10. The capture structure 8 has an outer substantially cylindrical surface 34 having a helically wound guide and advancement structure thereon which in the illustrated embodiment is a V-shaped thread 36 extending from adjacent the cylindrical surface 28 to adjacent an annular upper surface 38. The upper surface 38 is disposed substantially perpendicular to the axis of rotation A. A diameter of the cylindrical surface 34 measured between roots of the thread 36 is smaller than a diameter of the projected cylindrical surface 28. A diameter measured between crests of the thread 36 is illustrated equal to and may be smaller than the diameter of the cylindrical surface 28. Although a simple thread 36 is shown in the drawings, it is foreseen that other structures including other types of threads, such as buttress, square and reverse angle threads, and non threads, such as helically wound flanges with interlocking surfaces, may be alternatively used in place of the thread 36 in alternative embodiments of the present invention.

With particular reference to FIG. 7, the buttress stop feature 30 disposed near a base or bottom of the thread 36 is defined in part by the cylindrical surface 28 and in part by an upper shoulder 40 disposed perpendicular to the surface 28 and extending inwardly radially toward the thread 36. In a preferred embodiment, a buttress stop feature 42 disposed on the retaining structure 12 cooperates with the feature 30 as will be described more fully below to stop the advancement of the structure 12 along the thread 36 and provide for a desired placement of the structure 12 with respect to the capture structure 8.

A driving formation 44 extends from the upper surface 38 into the capture structure 8. The illustrated formation 44 includes six walls or facets 46 disposed parallel to the axis A and a hex-shaped seating surface or base 48 disposed perpendicular to the axis A. The driving formation 44 is sized and shaped to cooperate with a hex-driver for rotating and driving the shank body 6 into bone. It is foreseen that other driving features or apertures, such as slotted, tri-wing, hexalobular (such as the 6-point star shaped pattern sold under the trademark TORX), spanner, or the like may also be utilized according to the invention.

In the illustrated embodiment, the shank 4 is cannulated with a small central bore 49 extending an entire length of the shank along axis A. The bore 49 is coaxial with the threaded body 6 and the capture structure outer surface 34, providing a passage through the shank interior for a length of wire or pin inserted into the vertebra 16 prior to the insertion of the shank body 6, the wire or pin providing a guide for insertion of the shank body 6 into the vertebra 16.

Referring to FIGS. 1, and 8-10, the receiver 10 has a generally cylindrical outer profile with a substantially cylindrical base 50 integral with a pair of opposed upstanding arms 52 that extend from the base 50 to a top surface 54. The arms 52 form a U-shaped cradle and define a U-shaped channel 56 between the arms 52 and include an upper opening 57 and a lower seat 58 having substantially the same radius as the rod 21 for operably snugly receiving the rod 21.

Each of the arms 52 has an interior surface 60 that defines an inner cylindrical profile and includes a partial helically wound guide and advancement structure 62. In the illustrated embodiment, the guide and advancement structure 62 is a partial helically wound flangeform configured to mate under rotation with a similar structure on the closure top 18, as described more fully below. However, it is foreseen that the guide and advancement structure 62 could alternatively be a buttress thread, a square thread, a reverse angle thread or other thread like or non-thread like helically wound advancement structures for operably guiding under rotation and advancing the closure top 18 downward between the arms 52 and having such a nature as to resist splaying of the arms 52 when the closure top 18 is advanced into the U-shaped channel 56.

Tool engagement apertures 64 are formed on outer substantially cylindrical surfaces 66 of the arms 52 which may be used for holding the receiver 10 with a holding tool (not shown) having projections that are received within the apertures 64 during implantation of the shank body 6 into the vertebra 16. The apertures 64 may also cooperate with a holding tool during bone screw assembly and during subsequent installation of the rod and closure top. The illustrated apertures 64 are circular and disposed centrally on each arm 52. However, it is foreseen that the apertures may be configured in a variety of shapes and sizes and include undercut surfaces and be disposed at other locations on the arms 52, including near the top surfaces 54. Also, the holding tool (not shown) and respective apertures 64 may be configured to provide for a variety of ways to install the holding tool in the apertures, including a twist on/twist off engagement with the receiver, a twist on/snap off engagement or a flexible snap on/snap off engagement wherein the holding tool has legs which splay outwardly to position the tool for engagement in the apertures 64 or a combination thereof.

Communicating with the U-shaped channel 56 and located within the base 50 of the receiver 10 is a chamber or cavity 78 partially defined by an inner cylindrical surface 80, the cavity or chamber 78 opening upwardly into the U-shaped channel 56. In the illustrated embodiment, the cylindrical surface 80 has a diameter equal to an inner diameter between the arms 52 measured between crests of the guide and advancement structure 62. In the illustrated embodiment, the cylindrical inner surface 80 terminates at a ledge or lower shoulder 81 that is disposed perpendicular to an axis of rotation B of the receiver. The shoulder 81 is adjacent to a partial internal spherical seating surface 82 having a first radius. The surface 82 is sized and shaped for mating with the retaining structure 12, as described more fully below. It is foreseen that the surface 82 may be partially spherical, cylindrical, conical, tapered, or the like, and may include a high friction surface.

The base 50 further includes a restrictive neck 83 adjacent the seating surface 82. The neck 83 defines a bore 84 communicating with the cavity 78 and a lower exterior 86 of the base 50. The bore 84 is coaxially aligned with respect to the rotational axis B of the receiver 10. The bore 84 may be conically counterbored or beveled in a region 87 to widen the angular range of the shank 4. The neck 83 and associated bore 84 are sized and shaped to be smaller than a radial dimension of a fixed or fully expanded retaining structure 12, as will be discussed further below, so as to form a restriction at the location of the neck 83 relative to the retaining structure 12, to prevent the structure 12 from passing from the cavity 78 and out into the lower exterior 86 of the receiver 10 when the retaining structure 12 is seated on the seating surface 82. Again, it is foreseen that the retaining structure could be compressible (such as where such structure has a missing section) and could be loaded through the neck 83 and then allowed to expand and seat on the seating surface 82.

The retaining structure 12, best illustrated by FIGS. 1 and 5-7, has an operational central axis that is the same as the elongate axis A associated with the shank 4, but when the structure 12 is separated from the shank 4, the axis of rotation is identified as an axis C. The retaining structure 12 has a central bore 90 that passes entirely through the structure 12 from a top surface 92 to a bottom surface 94 thereof. An inner cylindrical surface 96 defines a substantial portion of the bore 90, the surface 96 having a helically wound guide and advancement structure thereon as shown by a v-shaped helical rib or thread 98 extending from adjacent the top surface 92 to near the bottom surface 94. Although a simple helical rib 98 is shown in the drawings, it is foreseen that other helical structures including other types of threads, such as buttress and reverse angle threads, and non threads, such as helically wound flanges with interlocking surfaces, may be alternatively used in an alternative embodiment of the present invention. The inner cylindrical surface 96 with the thread 98 are configured to mate under rotation with the capture structure outer surface 34 and helical guide and advancement structure or thread 36, as described more fully below.

The buttress stop formation 42 of the retaining structure 12 that is sized and shaped to mate with the stop 30 located on the shank 4 is located axially between the helical rib 98 and the bottom surface 94 of the structure 12. The formation 42 includes a lower shoulder 100 extending radially from the thread 98 and towards the structure 12 and a cylindrical wall 102 disposed perpendicular to the lower shoulder 100. The lower shoulder 100 is sized and shaped to mate and abut with the upper shoulder 40 and the cylindrical wall 102 is sized and shape to mate with the cylindrical projection 28. Thus, as will be described in more detail below, when the retaining structure 12 is rotated and mated with the capture structure 8 and fully installed thereon, the lower shoulder 100 of the structure 12 abuts the upper shoulder 40 of the stop 30. The retaining structure 12 and the capture structure 8 are configured such that when the buttress stop 30 abuts the buttress stop 42, the top surface 92 of the structure 12 is flush with the upper surface 38 of the capture structure 8. A sloped surface or chamfer 103 runs between the cylindrical wall 102 and the bottom surface 94 of the retaining structure 12.

It is foreseen that other types of geometrical orientation or structure may be utilized to engage or mate the capture structure and the retaining structure. For example, the capture structure may have an outer surface that is frusto-conical and the retaining structure may be a split ring with an inner surface sized and shaped to frictionally engage the frusto-conical capture structure. Also, the capture structure may have an inverted polyhedral or conical geometry and the mating retaining structure may be a plurality of pieces, the geometry of the pieces corresponding and cooperating with the polyhedral or conical geometry of the capture structure to frictionally envelope the retaining structure between the capture structure and an internal surface defining a cavity of the receiver. Furthermore, the retaining structure may be in the form of a band, collar or collet fixed or slidingly mateable with one or both the capture structure and the receiver.

The illustrated retaining structure 12 has a radially outer partially spherically shaped surface 104 sized and shaped to mate with the partial spherically shaped seating surface 82 of the receiver and having a radius approximately equal to the radius associated with the surface 82. The retaining structure radius is larger than the radius of the neck 83 of the receiver 10. Although not required, it is foreseen that the outer partially spherically shaped surface 104 may be a high friction surface such as a knurled surface or the like.

It is also foreseen that the retaining structure outer surface may be elliptical or ellipsoid in shape rather than spheroid in shape. Such an elliptical surface would be sized and shaped to contact and seat within a substantially spherical seating surface, such as the seating surface 82. Such an ellipsoid structure may be attachable to the shank upper portion by threads, a pin, compression, or the like as previously described with respect to the substantially spherical retaining structure 12. Furthermore, it is foreseen that an ellipsoid retaining structure may be integral with the bone screw shank and may include threads that allow the ellipsoid to be threadably received into a base of a bone screw receiver.

The illustrated retaining structure top surface 92 extends from the central bore 90 to the outer surface 104. The top surface 92 is disposed perpendicular to the axis of rotation C of the structure 12. The bottom surface 94 extends from the chamfer 103 to the outer surface 104 and also is disposed perpendicular to the axis of rotation C.

As previously disclosed herein, in the illustrated embodiment, the outer partially spherically shaped surface 104 of the retaining structure 12 slidingly mates with the spherically shaped seating surface 82 of the receiver. It is foreseen that in other embodiments according to the invention, the retaining structure may be in fixed relation with the receiver but in slidable relationship with the shank or capture structure of the shank, for example, the retaining structure may be in the form of a toroid or ring attachable to the receiver, for example, a compressible or split cylinder with a through bore, the outer cylindrical portion being sized and shaped to fit within a recess or groove of the receiver. Such a retaining structure may be uploaded into the receiver along with the shank and then snapped or otherwise fixed into place near a base of the receiver, the retaining structure thus capturing a portion of the shank within the receiver, the shank being pivotable with respect to both the retaining structure and the receiver. Such a retaining structure may include an inner spherical, conical or otherwise curved surface slidingly, frictionally mateable with a captured portion of the shank.

The elongate rod or longitudinal member 21 that is utilized with the assembly 1 can be any of a variety of implants utilized in reconstructive spinal surgery, but is normally a cylindrical elongate structure having a smooth, outer cylindrical surface 108 of uniform diameter. The rod 21 is preferably sized and shaped to snugly seat near the bottom of the U-shaped channel 56 of the receiver 10 and, during normal operation, is positioned slightly above the bottom of the channel 56 at the lower seat 58.

One example of the compression structure 14 is illustrated in FIGS. 1-4. In the embodiment shown, the compression structure 14 includes a body 110 of substantially circular cross-section integral with a pair of upstanding arms 112. The body 110 and arms 112 form a generally U-shaped, open, through-channel 114 having a substantially U-shaped longitudinal connecting member receiving and seating surface 116 having a radius substantially conforming to a radius of the rod 21 and thus configured to operably snugly engage the rod 21. The arms 112 disposed on either side of the channel 114 each included a top surface 118 that is parallel to an annular bottom surface 120. The compression structure 14 includes a substantially cylindrical outer surface 122 and an inner cylindrical wall 124 defining a central through-bore 125 extending along a central axis D of the compression structure 14. The top surface 118 and the bottom surface 120 are disposed perpendicular to the axis D. Extending between the inner cylindrical wall 124 and the bottom surface 120 is a curved or spherical surface 126 sized and shaped to frictionally engage and mate with the outer spherical surface 104 of the retaining structure 12. The cylindrical surface 122 has a diameter slightly smaller than a diameter between crests of the guide and advancement structure 62 allowing for top loading of the compression structure 14 as illustrated in FIGS. 8-10. The cylindrical surface 122 diameter and a height of the compression structure 14 measured from the top surface 118 to the bottom surface 120 are sized such that the compression structure 14 is received within the cylindrical surface 80 of the receiver 10 below the guide and advancement structure 62, but the bottom surface 120 thereof does not engage the ledge 81 when fully installed on the retaining structure 12. There is thus a space between the bottom surface 120 and the ledge 81 in any angular position of the shank 4 with respect to the receiver 10. When fully installed, the compression structure 14 does not contact the bone screw shank capture structure 8, but engages only with the retaining structure 12. When pressed upon by the rod 21, the surface 126 of the compression structure 14 frictionally engages the surface 104 of the retaining structure 12, which in turn presses upon the seating surface 82 of the receiver 10. In some embodiments, the compression structure could be up-loaded into the receiver, followed by up-loading of the retaining structure into the receiver. It is also foreseen that the in other embodiments according to the invention, the compression structure may have other geometries depending upon the geometry of the retaining structure and the shank upper portion. For example, in an embodiment in which the retaining structure is in the form of a ring that is fixed to a receiver, a lower surface of the compression structure may extend substantially around the shank upper portion, or on the other hand, form a crown near an upper surface of the shank, thereby complimenting the particular geometry of the shank upper portion. This may be in the form of flat, spherical, conical, or otherwise curved or complimentary shaping of the compression structure lower surfaces for pressing directly against a shank upper portion.

Because the receiving surface 116 is sized and shaped to snugly receive the cylindrical rod surface 108, the surface 116 is substantially symmetrical, having a base line or portion 130 that may also be described as a lower vertex or bottom seat area that intersects a plane running through the axis D substantially equidistant from the arms 52 and is disposed substantially opposite a central portion of the upper opening of the channel 57 when the structure 14 is fully seated in the receiver 10. A pair of substantially similar curved side or lateral surfaces 132 are disposed on either side of the base portion or lower vertex 130 and extend upwardly away from the base 130 and toward the top surfaces 118. The pointed or sharply edged projections 15 are disposed on the side surfaces 132, typically in pairs, such that each pair of projections 15 located substantially opposite and facing one another. The pointed projections 15 are located such that when the compression structure 14 is fully seated in the receiver 10 the pointed projections 15 are located above the lower seat 58, that is between the lower seat 58 and the guide and advancement structure 62. The embodiment illustrated in FIGS. 1-14 shows two pairs of projections 15 substantially equally spaced, with two projections on each side of the base line or portion 130. It is foreseen that fewer or greater numbers of projections may be provided. Whether there is one projection or a plurality of projections, each projection is substantially pointed toward an axis of the rod 21 when captured by the receiver 10 and pushed toward the base 130 by the closure structure 18, such that the points or edges of the projection or projections 15 extend substantially radially into the rod surface 108, penetrating the rod surface 108 and thereby fixing the rod 21 to the rod receiving surface 116 of the compression structure 14. The pointed projections 15 illustrated in FIGS. 1-14 are integral with the compression structure 14. Similar to the embodiment shown in FIGS. 21-23, it is foreseen that the projections may be removably fixable to the rod receiving surface 116. The illustrated projections 15 are polyhedral in form with triangular sides and a common vertex. It is foreseen that projections according to the invention may also have other shapes, such as a cone shape with a circular or oval base with sides tapering to a point, or a wedge shape with sides tapering to an edge. It is also foreseen that projections or points according to the invention may be in the form of a knurling or roughened surface portion or portions on the rod receiving surface 116. Furthermore, knurling or roughening of the surface 116 may be utilized in combination with spikes, cleats or other projections that point somewhat off axis of the longitudinal connecting member.

With particular reference to FIGS. 12-14, the closure structure 18 can be any of a variety of different types of closure structures for use in conjunction with the present invention with suitable mating structure on the upstanding arms 52 of the receiver 10. The closure structure 18 is rotatable between the spaced arms 52. The illustrated structure 18 includes a cylindrical base 140 and a break-off head 142. Helically wound about the base 140 is a guide and advancement structure in the form of a flange form 144. The illustrated guide and advancement structure 144 operably joins with the guide and advancement structure 62 disposed on the interior 60 of the arms 52. The flange form 144 includes a root 146 and a crest 148. Furthermore, the flange form 144 also has a trailing surface 150 and a leading surface 152 which are relative to the forward movement of the closure 18 as it is rotated clockwise about the central axis B of the bone screw receiver and joined therewith. Located on the trailing surface 150 or the leading surface 152 or both is a projection which protrudes rearwardly or frontwardly with respect to the width of the flange form 144 at the root 146 and which interlocks with the guide and advancement mating structure 62 of the receiver 10.

In the illustrated embodiment, the flange form 144 has a protrusion 154 that projects rearwardly from the trailing surface 150. The flange form 144 utilized in accordance with the present invention may be any structure which effectively locks the closure 18 to the structure within which it is set so as to prevent splaying of the structure upon which mating guide and advancement structure is mounted. Various flange form structures which can be used alternatively are illustrated in applicant's U.S. Pat. No. 6,726,689, which is incorporated herein by reference. As stated herein with respect to the flange form guide and advancement structure 62, it is also foreseen that according to the invention the guide and advancement structure 144 could alternatively be a buttress thread, a square head, a reverse angle thread or other thread like or non-thread like helically wound advancement structure for operably guiding under rotation and advancing the closure 18 downward between the arms 52 and having such a nature as to resist splaying of the arms 52 when the closure top 18 is advanced into the U-shaped channel 56.

The base 140 of the closure structure 18 includes a lower surface 156 having a dome 158 located thereon. The dome 158 extends greatest from the base 140 along a central axis E that is operably coaxial with the receiver axis B. The dome 158 in the present embodiment is spherical in shape and, in particular, is a partial sphere that has a uniform or constant radius of generation.

However, it is foreseen that in certain embodiments the radius may vary depending upon the needs and desires of the particular structure and the dome 158 may have shape that is only partly a spherical curved surface or some other shape. The dome 158 may be a simple curved surface that allows greatest projection along the axis. That is, the dome surface could be radiused at the location of greatest projection and feathered along the periphery so as to not have a continuous uniform radius of generation throughout, but rather a continually changing radius of generation along at least the length thereof. Preferably, the dome 158 is smoothly curved where the dome 158 intersects with the axis E. It is also foreseen that the lower surface 156 could be flat or have a point and rim geometry.

The closure structure 18 break off head 142 is secured to the base 140 by a break off region 160 that is designed to allow the head 142 to break from the base 140 at a preselected torque, for example, 70 to 140 inch pounds. The break off head 142 has an external radial outward surface with six planar facets 162 so as to form a structure designed to be received within a socket of a driving type tool (not shown) with a similar receiving shape. The break off head 142 has a central bore 164 that may also include driving formations suitable for engagement by a tool (not shown).

During installation, the dome 158 engages the rod 21 at an apex 166 as seen in FIGS. 13 and 14. The closure structure 18 is torqued until a preselected pressure is reached at which point the closure 18 at the apex 166 abuts the rod 21 which in turn is urged toward but not completely to the lower seat 58 of the channel 56. In turn, the rod 21 braces against the compression structure 14 which urges the retaining structure 12 to fixedly seat in the cavity 78. As the rod 21 moves into contact with the compression structure 14, the four projections 15 penetrate the rod surface. Thereafter, the receiver 10 is no longer rotatable relative to the shank 4, but rather is locked in position.

The closure structure 18 also includes removal tool engagement structure which in the present embodiment is in the form of a hex-shaped and axially aligned aperture 168 disposed in the base 140, as shown in FIG. 13. The hex aperture 168 is accessible after the break-off head 142 breaks away from the base 140. The aperture 168 is coaxial with the helically wound guide and advancement structure 144 and is designed to receive a hex tool, of an Allen wrench type, into the aperture 168 for rotating the closure structure base 140 subsequent to installation so as to provide for removal thereof, if necessary. Although a hex-shaped aperture 168 is shown in the drawings, the tool engagement structure may take a variety of tool-engaging forms and may include more than one aperture of various shapes, such as a pair of spaced apertures, a left hand threaded bore, an easy out engageable step down bore or the like.

With reference to FIG. 1, prior to the polyaxial bone screw assembly 1 being implanted in the vertebra 16, the retaining structure 12 is typically first inserted or top-loaded in this embodiment, into the receiver U-shaped channel 56, and then into the cavity 78 to dispose the structure 12 adjacent the inner surface 80 of the receiver 10. The structure 12 may be loaded with the axis C coaxial with the receiver axis B or turned or rotated such that the axis C is perpendicular to the axis B of the receiver 10 during insertion of the structure 12 into the receiver 10. Then, after the retaining structure 12 is within the cavity 78, the retaining structure 12 is rotated approximately 90 degrees such that the axis C is coaxial with the axis B of the receiver 10, and then the structure 12 is seated in sliding engagement with the seating surface 82 of the receiver 10.

The shank capture structure 8 is preloaded, inserted or bottom-loaded into the receiver 10 through the bore 84 defined by the neck 83. The retaining structure 12, now disposed in the receiver 10 is coaxially aligned with the shank capture structure 8 so that the helical v-shaped thread 36 rotatingly mates with the thread 98 of the retaining structure 12. As previously discussed herein, other types of retaining structures and other ways of mating or coupling such structures with the shank may be utilized in bone attachment assemblies according to the invention.

With reference to FIGS. 5-7, the shank 4 and/or the retaining structure 12 are rotated to fully mate the structures 36 and 98 along the respective cylindrical surfaces 34 and 96, fixing the capture structure 8 to the retaining structure 12, until the lower shoulder 100 of the buttress stop 42 abuts the upper shoulder 40 of the stop 30.

With reference to FIGS. 8-10, at this time the shank 4 is in slidable and rotatable engagement with respect to the receiver 10, while the capture structure 8 and the lower aperture or neck 83 of the receiver 10 cooperate to maintain the shank body 6 in rotational relation with the receiver 10. According to the illustrated embodiment, only the retaining structure 12 is in slidable engagement with the receiver seating surface 82. Both the capture structure 8 and threaded portion of the shank body 6 are in spaced relation with the receiver 10. The shank body 6 can be rotated through a substantial angular rotation relative to the receiver 10, both from side to side and from front to rear so as to substantially provide a universal or ball joint wherein the angle of rotation is only restricted by engagement of the neck 26 of the shank body 6 with the neck or lower aperture 83 of the receiver 10.

In the embodiment shown, the compression structure 14 illustrated in FIGS. 1-4 is then loaded into the receiver 10 as illustrated in FIGS. 8-10. With particular reference to FIG. 8, the insert U-shaped channel 114 is aligned with the receiver 10 U-shaped channel 56 and the compression structure 14 is initially top or down-loaded into the receiver 10 until the arms 112 are disposed adjacent to the surface 80 and the bottom spherical surface 126 is in contact with the surface 104 of the retaining structure 12. To ready the assembly 1 for implantation into bone, the shank 4, receiver 10 and compression structure 14 axes A, B and D, respectively are aligned, providing access to the hex-shaped formation 44 on the shank capture structure 8 through the bore 125 of the compression structure 14. Such placement allows for unrestricted rotation of the shank body 6 with respect to the receiver 10.

With reference to FIG. 11, the assembly 1 is typically screwed into a bone, such as the vertebra 16, by rotation of the shank 4 using a driving tool with an Allen type driving formation 175 that operably drives and rotates the shank 4 by engagement thereof with the shank at the driving formation 44, a base 177 of the tool 175 abutting and engaging the driving formation 44 at the base 48 thereof. It is foreseen that in other embodiments according to the invention, the hex-shaped driving formation 44 may be replaced by other types of foot print type tool engaging formations or recesses. Through the driving formation aperture, the retaining structure and the shank can be crimped together so as to not come apart with rotation.

Typically at least two and up to a plurality of bone screw assemblies 1 are implanted into vertebrae for use with the rod 21. Each vertebra 16 may be pre-drilled to minimize stressing the bone. Furthermore, when a cannulated bone screw shank is utilized, each vertebra will have a guide wire or pin (not shown) inserted therein that is shaped for the bone screw cannula 49 of the bone screw shank and provides a guide for the placement and angle of the shank 4 with respect to the vertebra 16. A further tap hole may be made using a tap. The shank body 6 is then driven into the vertebra 16, by rotation of the driving tool 175.

With reference to FIGS. 12-14, the rod 21 is eventually positioned within the receiver U-shaped channel 56, and the closure structure is then inserted into and advanced between the arms 52. The compression structure 14 is pressed downwardly into engagement with the retaining structure outer surface 104 to set the angle of articulation of the shank body 6 with respect to the receiver 10 by pressure from the rod 21 that in turn is being pressed upon by the dome 158 of the closure structure 18. The rod 21 is seated on the compression structure 14, with one or more of the projections 15 engaging the rod surface 108 and the fastener 18 is initially placed between the arms 52 and rotated using an installation tool (not shown) engaged with the surfaces 162 of the break-off head 142 until the guide and advancement structure 144 is fully mated with the receiver guide and advancement structure 62. With reference to FIG. 13, the break-off head 142 is then twisted to a preselected torque, for example 70 to 140 inch pounds, also utilizing the installation tool in engagement with the faceted outer surface 162 of the break-off head 142, with or without bending of the rod 21 in order to achieve and maintain a desired alignment of the spine. As illustrated in FIGS. 13 and 14, upon final installation, a stable fixation of the rod 21 is accomplished with one area of contact provided at the apex 166 of the closure top dome 158 and at least two areas of contact provided between the rod 21 and the compression structure 14 at least two or more projections 15 with such projections penetrating the rod surface 108.

If removal of the assembly 11 is necessary, or if it is desired to release the rod 21 at a particular location, disassembly is accomplished by using an Allen type tool (not shown) with the hex-shaped driving formation 168 located on the closure structure base 140 to rotate and remove the closure structure base 140 from the receiver 10. Disassembly of the assembly 1 is accomplished in reverse order to the procedure described previously herein for assembly. Again, it is foreseen that a non-break off closure could be used which is inserted and removed with the same driving formation. Also, other types of closure and locking mechanisms may be utilized with assemblies according to the invention, including, for example, slide-on caps.

With reference to FIGS. 15-20 an alternative open-ended fixed bone screw 201 according to the invention is illustrated and shown with a closure structure 202 and a longitudinal connecting member, shown as a rod 206. The illustrated rod 206 is solid and has an outer substantially cylindrical surface 208.

The bone screw 201 includes a threaded shank 212 integral with a receiver 214 having a pair of opposed arms 216 that form a yoke 218. The yoked arms 216 define a central slot or channel 220 defined in part by a curved, U-shaped rod-receiving surface 222 with a plurality of pointed projections or cleats 224 extending radially inwardly. Each arm 216 includes an inner surface 226, a portion of which has a guide and advancement structure sized and shaped to cooperate with reciprocal guide and advancement structure on the closure structure 202.

The receiving surface 222 is sized and shaped to snugly receive the cylindrical rod surface 208 and thus is substantially symmetrical, having a base line or bottom seat area 230 disposed substantially opposite a center of the upper opening of the channel 220 and a pair of substantially similar curved side surfaces 232 disposed on either side of the bottom 230 and extending upwardly away from the base line and toward the arms 216. Preferably, the pointed projections 224 are disposed on the side surfaces 232 in pairs such that each pair of projections 224 is located substantially opposite and facing one another. The embodiment illustrated in FIGS. 15-20 shows two pairs of projections 224 substantially equally spaced, with two projections on each side of the base 230. It is foreseen that fewer or greater numbers of projections may be provided. Whether there is one projection or a plurality of projections, each projection in this embodiment is substantially pointed toward an axis of the rod 206 when captured by the receiver 214 and pushed toward the seat 230 by the closure structure 202, such that the points of the projection or projections 224 extend radially into the rod surface 208, penetrating the rod surface 208 and thereby fixing the rod 206 to the rod receiving surface 222 of the receiver 214. The pointed projections 224 illustrated in FIGS. 15-20 are integral with the receiver 214. The illustrated projections 224 are polyhedral in form with triangular sides tapering to a common vertex or point. It is foreseen that projections according to the invention may also have other shapes, such as a cone shape with a circular or oval base with sides tapering to a point, or a wedge shape with sides tapering to an edge.

With particular reference to FIG. 15 and FIGS. 18-20, the closure structure 202 can be any of a variety of different types of closure structures for use in conjunction with the present invention with suitable mating structure on the upstanding arms 216 of the receiver 214. The closure structure 202 is rotatable between the spaced arms 216. The illustrated structure 202 includes a cylindrical base 240 and a break-off head 242. Helically wound about the base 240 is a guide and advancement structure in the form of a flange form 244. The illustrated guide and advancement structure 244 operably joins with a guide and advancement structure 245 disposed on the interior of the arms 216. The closure structure flange form 244 is substantially similar to the closure structure flange form 144 discussed previously herein. Furthermore, the closure structure 202 includes a break-off region 260, facets 262, tool receiving bore 264 and removal aperture 268 substantially identical or similar to the respective break-off region 160, facets 162, tool receiving bore 164 and removal aperture 168 discussed previously herein with respect to the closure structure 18 and incorporated by reference herein with respect to the closure structure 202. The closure structure 202 differs from the closure structure 18 with respect to a bottom surface 270 that contacts and presses against the rod 206. The surface 270 is not domed shaped like the surface 158 of the structure 18, but rather is planar, providing a flat contact surface for the rod curved surface 208.

In use, the bone screw 201 is implanted into a vertebra using a driving tool (not shown) that engages outer surfaces and tool receiving apertures 280 of the arms 216. Eventually, the rod 206 is implanted and received in the channel 220, followed by insertion and tightening of the closure structure 202 in the receiver 214 in a manner as described previously herein with respect to the closure structure 18. Continued rotation of a closure structure driving tool (not shown) advances the closure structure 202 into the channel 220 so that the lower surface 270 engages the rod 206 and pushes the rod 206 toward the rod receiving surface 222, causing the pointed projections 224 to engage and penetrate the rod surface 208. In this manner, the pointed projections 224 cooperatively form a four-point anchor, cooperating with the closure structure surface 270 and securing the rod 206 against rotation, axial movement and inadvertent dislodgment of the rod 206 from the bone screw 201.

As shown in FIGS. 18-20, the bone screw 201 is effectively utilized for securing the rod 206 within the bone screw channel 220 against translational and rotational motion. It is further noted that the illustrated rod 206 is bendable by tools well known in the art and is generally circular in cross-section. In the illustrated embodiment, the rod 206 may be bent to be non-linear at the location where the rod 206 is positioned over the rod-receiving surface 222. Thus, the rod 206 may present a surface that is curved both axially and circumferentially within the bone screw yoke 218. In particular, because of the axial curvature of the rod 206, upon installation, the rod 206 rests in the bone screw channel 220 so that only a central portion of the rod surface 208 makes contact with the channel bottom 230, while a remainder of the surface 208 within the sides of the bone screw curves away, so as to be in spaced relationship from the bottom surface 230. In such an arrangement, the pointed projections 224 abrade and/or penetrate the rod surface 208 adequately prohibiting translational and rotational movement of the rod 206.

With reference to FIGS. 21-23, another alternative embodiment 301 of a fixed bone screw according to the invention, substantially similar to the bone screw 201 is illustrated. The bone screw 301 is shown with an elongate longitudinal connecting member in the form of a rod 306 having an outer cylindrical surface 308 and further shown with a closure structure 302. The rod 306 is identical or substantially similar to the rod 206 previously described herein and the closure structure 302 is identical or substantially similar to the closure structure 202 previously described herein.

The bone screw 301 includes a shank 312 and a receiver 314. The receiver 314 has a longitudinal connecting member receiving surface 322 substantially similar to the receiving surface 222 previously discussed herein with respect to the receiver 214 of the bone screw 201. However, the bone screw 301 includes pointed projections 324 that are attachable and removable from the receiving surface 322. The pointed projections 324 are otherwise similar to what has been previously described herein with respect to the projections 224 and the projections 15. With particular reference to FIG. 23, the projections 324 and the receiving surface 322 in the illustrated embodiment are sized and shaped such that a lower portion 340 of each projection 324 is press fit into a respective aperture 342 formed in the receiving surface 322, resulting in a frictional engagement between the projection 324 and the surfaces of the receiver 314 forming the aperture 342. It is foreseen that the projections 324 may be attached to the receiving surface 322 by other means such as by using grooves, threads or adhesives. Furthermore, the removable pointed projections 324 allow the rod-receiving surface 322 to be equipped and customized with points 324 of varying properties such as degree of sharpness or hardness depending upon desired use.

It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown. 

1. In a bone attachment structure having a receiver member with a pair of spaced arms defining an open channel for receiving a longitudinal connecting member, the longitudinal connecting member being captured in the receiver by a closure structure, the improvement comprising: a) a longitudinal connecting member receiving surface facing the open channel, the receiving surface having a base portion and at least one side portion disposed laterally of the base portion; and b) at least one projection extending from the at least one side portion, the projection having a sharp end.
 2. The improvement of claim 1 wherein the projection sharp end is directed substantially radially inwardly toward an axis of a longitudinal connecting member when the connecting member is received in the channel and pressed toward the receiving surface by a closure structure.
 3. The improvement of claim 1 wherein the at least one projection is a first pointed projection and further comprising a second pointed projection and the at least one side portion is a first side portion and further comprising a second side portion, the first pointed projection extending from the first side portion and the second pointed projection extending from the second side portion.
 4. The improvement of claim 3 wherein the side portions have at least four projections.
 5. The improvement of claim 1 wherein the longitudinal connecting member receiving surface is on the receiver.
 6. The improvement of claim 1 wherein the longitudinal connecting member receiving surface is on a compression member disposed in the receiver.
 7. The improvement of claim 6 wherein the bone attachment structure is a polyaxial bone screw having a shank with an upper portion disposed in the receiver, the upper portion having a formation sized and shaped for engagement with a bone screw driver for driving the shank into bone, the compression member having an aperture sized and shaped for receiving the driver therethrough.
 8. The improvement of claim 6 wherein the projection is integral with the compression member.
 9. The improvement of claim 1 wherein the bone attachment structure is a bone screw having a shank with the receiver being integral with the shank.
 10. The improvement of claim 1 wherein the projection is integral with the receiver.
 11. The improvement of claim 1 wherein the projection is removably fixable to the receiving surface.
 12. The improvement of claim 1 wherein the receiving surface is U-shaped.
 13. The improvement of claim 1 wherein the bone attachment structure is a bone screw with a cannulated shank.
 14. In a polyaxial bone screw assembly having a receiver with a pair of spaced arms defining an open channel for receiving a longitudinal connecting member, the longitudinal connecting member being captured in the receiver by a closure structure, the improvement comprising: a) a compression structure insertable in the receiver with a central bore and a surface facing a rod receiving channel; and b) at least one pointed projection extending from the compression structure surface and extending into the channel.
 15. The improvement of claim 14 wherein the compression structure has at least two pointed projections and the closure structure has a domed shaped rod engaging surface.
 16. The improvement of claim 14 wherein the closure structure has a substantially flat rod engaging surface.
 17. The improvement of claim 14 wherein the at least one pointed projection is a first pointed projection and further comprising at least a second pointed projection disposed substantially opposite and facing the first pointed projection.
 18. The improvement of claim 14 wherein the pointed projection is integral with the compression member.
 19. The improvement of claim 14 comprising at least four pointed projections.
 20. The improvement of claim 14 further comprising a cannulated bone screw shank.
 21. A polyaxial bone screw assembly comprising: a) a receiver defining a central bore and having a top portion and a bottom portion, the top portion having a flange form, the bottom portion defining a chamber communicating with the central bore and having a bottom opening, the bottom opening having a diameter; b) a shank having an upper portion and a lower portion for fixation to a bone, the upper portion having a width smaller than the receiver bottom opening diameter; c) an independent retaining structure in contact with the shank upper portion, the retaining structure having a contact surface configured for slidable engagement with the receiver at the bottom portion defining the chamber; d) a compression structure insertable in the receiver and pressable against the retaining structure, the compression structure having a central bore and a surface facing a rod receiving channel; and e) at least one pointed projection extending from the compression structure surface and extending into the channel.
 22. The assembly of claim 21 wherein the retaining structure contact surface is substantially spherical.
 23. The assembly of claim 21 wherein the flangeform is a discontinuous flangeform disposed on first and second inner arms of the receiver.
 24. The assembly of claim 23 further comprising a closure structure having a continuous flangeform mateable with the discontinuous flangeform.
 25. The assembly of claim 24 wherein the closure structure has a domed shaped rod engaging surface and the compression structure has at least two pointed projections.
 26. The assembly of claim 21 wherein the shank upper portion has a tool receiving recess.
 27. The assembly of claim 26 wherein the tool receiving recess is hex-shaped.
 28. The assembly of claim 21 wherein the retaining structure has a first substantially spherical outer surface and the compression structure has a second spherical surface sized and shaped to engage the first spherical surface.
 29. The assembly of claim 21 wherein the at least one pointed projection is a first pointed projection and further comprising a second pointed projection disposed substantially opposite and facing the first pointed projection.
 30. The assembly of claim 21 wherein the pointed projection is integral with the compression member.
 31. The assembly of claim 21 comprising at least four pointed projections.
 32. The assembly of claim 21 wherein the bone screw shank is cannulated. 